Method of treating absorber solutions used in gas purification



, E; J. MQCREARY 2,890,931 METHOD oF TREATING ABsoRBER soLuTIoNs usen 1NGAS PURIFICATION 2 Sheets-Sheet 1 Filed NOV. '1.8, 1955 A T TRNE K9 June16, 1959 E. J. MCCRVEARY Y 42,890,931

METHOD oF TREATING ABsoRBER soLuTIoNs USED 1N GAs PURTFICATION e9 een gINVENToR.

` EJ. MccRE-ARY BY E A TTORNEVS Unite METHOD F TREATING ABSGRBERSOLUTIONS USED IN GAS PURIFICATION Elmer J. McCreary, Bartlesville,Okla., assignor to Phillips Petroleum Gompany, a corporation of DelawareThis invention relates to a method of treating absorber solutions usedin gas purification.

In the purification of gases, particularly, natural gas, wherein acidiccompounds such as hydrogen sulfide and carbon dioxide are removed,dificulties are encountered in reactivating the absorber solution. Inparticular, where natural gas is treated with a monoethanolarninesolution, it is rather difficult to reactivate the solution by ordinaryfractionation; Proper control of the temperature of the monoethanolaminesolution during reactivation is also quite important in that attemperatures above about 300 F., a slow decomposition of the solutiontakes place with the formation of extremely corrosive decompositionproducts.

In accordance with one important aspect of the invention, a richmonoethanolamine treating solution is heated by indirect heat exchangeto a temperature of about 245 F. and then contacted withlive steam whilemaintaining a temperature in the neighborhood of 275 F. and preventingtemperature rise to 290 or 300 F.` i

In another important aspect of the invention, contacting between steamand an absorbent `solution is effected within a special type of treatingvessel. In this vessel, the rich treating solution is sprayed intocontact with steam previously used to remove the acidic compounds fromrelatively purified amine solution. This spray contacting effectivelyremoves the major part of the acidic compounds which are discharged to aflare. Thereupon the partially purified treating solution contacts puresteam and passes concurrently therewith through a suitable contactingdevice, such as a series of perforated trays. This results in veryeffective removal of the acidic compounds from the treating solutionwithout formation of corrosive decomposition products.

In still another aspect of the invention, the gaseous effluent from thecontacting zone is passed through an ejector to provide a reducedpressure in a storage vessel for the purified amine solution, and thewater contained in this stream is efiiciently recovered as ademineralized water product.

Accordingly, it is `an object of the invention to provide an improvedmethod of purifying absorber materials used in the purication of gas. tq It is a` further object to provide eflicient Contact between the richabsorber material and steam while prevening the temperature fromreaching a value which would result in the formation of undesirablecorrosive decomposition products.

lt is a still further object to economically recover the water andenergy content of the gaseous effluent from the purification step.

It is a further objet to provide an efcient, low cost system forpurifying natural gas.

Various other objects, advantages and features of `the invention willbecome apparent lfrom the following de- States Patent O taileddescription taken in conjunction with the accompanying drawing, inwhich:

Figure 1 is a tlovv diagram of a gas recovery system constructed inaccordance with the invention;

Figure 2 is a vertical, sectional view, partly in elevation, of thecontacting device;

Figure 3 is a flow diagram of a modified purification system; and

Figure 4 is a detailed view of a portion of the apparatus shown byFigure 3.

Referring now to Figure l, the gas to be purified is fed through a line10 to an absorber column 11 wherein it is contacted with an absorbersolution, such as monoethanolamine, diethanolamine, triethanolamine,mixtures of these amines or other aqueous alkaline solutions which isintroduced through a line 12.. The purified gas, substantially free ofacidic compounds, is withdrawn overhead by a line 13, and the richabsorber material, containing acidic compounds, such as hydrogensulfide, carbon dioxide and mercaptans, is withdrawn by a line 14.

The rich solution passes successively through heat exchangers 15 and 16which heat it, by increments, to a temperature within the range of 240to 265 F. A motor valve 17 operatively connected to a liquid levelcontroller 18 feeds the rich solution to a contacting vessel 19 at arate controlled to maintain a predetermined liquid level in the absorbercolumn 11.

Within the vessel 19, the rich solution is contacted with steam which is-admitted to the contacting vessel from a line 20 under the control of amotor valve 21 operatively connected to a pressure recorder controller22 having a sensing element 23 in the line 20. The controller 22maintains a predtetmined pressure of about 45 p.fs.i.a. in the bottomand 43 p.s.i.a. and 271 F. in top of the contacting vessel, `and thesteam addition is carefully controlled to maintain a temperature of 260to 290 F. Within the contacting vessel.

In the vessel 19, as will be more fully described here inafter, theabsorber solution is puried. and freed of acidic compounds, the purifiedliquid being withdrawn through a line 25 under the control of a motorvalve 2d which is operatively connected to a liquid level controller 27.This controller regulates the flow of purified solution into a storagedrum 28 at such a rate as to maintain a predetermined liquid levelwithin the contacting vessel 19. p A purified solution is withdrawn, asrequired, from the drum 28 and passes through a line 2:9, a pump 30, theheat exchanger 15 and a cooler 31 to the absorber solution inlet 12 ofthe column 11.

A gaseous stream, containing steam and the acidic compounds removed fromthe absorber solution, leaves the vessel 19 through a line 34 and passesto a drip tank 35 wherein some of the steam is condensed and entrainedliquid (H2O plus amine) separates into a liquid phase within the vessel.This liquid, which contains small quantities of treating solution, iswithdrawn through a line 36 under the control of a motor valve 37operatively connected to a liquid level controller 3S. This materialdischarges through a line 36 to the drum 2S at a rate determined bycontroller 38 to maintain a desired liquid I level within the tank 35.

At the top thereof, Ithe tank 35 is provided with wire mesh or otherforms of mist extractors .39 to prevent liquid `entrainment in the gasleaving the tank, and this material, which is essentially a mixture ofsteam and the acidic compounds substantially denuded of treatingsolution, is passedthrough an ejector 40. The ejector 40 has a pressurereduction line 41 extending into the drum 28 `so that the pressure ofthe gas is utilized to provide a desiredereduced pressure within thestorage drum"2`8`,

From the ejector 40 the gaseous materialpasses to" a condenser 43wherein rsubstantially 'all of the Water vapor y is condensed, theacidic sulfur gases passing through a line 44 under the control of amotor valve 45 operatively connected to a pressure indicator controller46 having a sensing element 47 in the line 44, Thereupon, the gases aredischarged to a-are or other suitable disposal, as desired, and thecontroller 46 maintains a predetermined back pressure on the system.

lThe condensate from unit 43 passes through Ia line 48 to an accumulator49 from which a demineralized water product is withdrawn through a line50 and passed through a pump 51 either to a steam generator or, as.required, through a valved line 52 to the storage drum 28.

Steam is passed to the heat exchanger 16 by a line 53 which, in turn, isconnected by a steam trap 54 and a line 55 to the accumulator 49.V Thisconnection insures the presence of steam in the exchanger 16, andpermits recovery of the condensate as a demineralized water product. t Y

In the foregoing description it will be noted that the rich absorbersolution is eiectively puriied by Virtue of the eicient contact betweenthe steam and rich absorber solution. Moreover, the energy, watercontent, and treating solution of the eluent from the contacting vesselare all very eiciently recovered. Finally, the temperature is controlledto obtain most efficient purication of the absorber solutionwithout theformation of corrosive decomposition products or dilution of thetreating solu-tion.

The contacter 19 of Figure 1 is shown in more detail by Figure 2. Itwill be noted that the rich absorbent solution enters the vessel nearthe top through a generally horizontal pipe 58 having a series ofupwardlydirected perforations 59 interiorly of the vessel. This spray iscontacted with steam within a chamber 60 dened by plates 61, 62 and 63,the steam having previously contacted a relatively purified absorbersolution. Due to the maintenance of a temperature of 260 to 290 F.within the vessel, the acidic compounds are efticiently stripped fromthe absorbent solution and passed as `a gas through an outlet pipe 65yat the top of the vessel.

The partially purified yabsorber liquid passes through a downcomer 66'and a liquid trap 67 to a chamber 68 where it is contacted With livesteam introduced through a conduit 70. The steam `and partially purifiedliquid flow concurrently through two sets 71 yand 72 of contacting traystoward the bottom of the vessel. This con-tact between the steam andsolution efficiently removes the remaining acidic compounds from theabsorbent material which ows downwardly through a pipe 73 to the bottompart of the vessel. The steam, after contacting the solution in thetrays 71 and 72, passes upwardly through passages 74 and 75 to thechamber 60 where it contacts the incoming rich solution, as previouslydescribed. Suitable baflles are provided in the vessel to confine thellow of steam in the manner stated, and it will be observed that thesteam can flow into the regions 76 and 77 ot the vessel to maintain thecontacting step at the prescribed temperature.

The contacting action effected within the vessel 19 as thus described,is much more eiiicient and provides a purer product than wouldcontacting of the materials in an ordinary stripper column.

As a specic example of the application of the process, there can bementioned the purilication of a monoethanolamine solution used tovremove acidic gases from sour natural gas. It is to be understood,however, that the invention is not to be restricted to this particulartype of treatment but is applicable to other gas absorption agentssuitable for removing impurities from gas streams.

In this specific embodiment, 100 gallons per minute of a 15 percentaqueous solution of monoethanolamine containing hydrogen sulfide andother acidic compounds removed fromthe natural gas passes through line14 and heat exchangers 15, 16 wherein it is raised to atemperav2,890,931 i l ture of 245 F. 45 pounds p.s.i.a. of steam entersthe vessel 19 in sufficient quantities to raise the temperature to 274F. bottom land 272 F. top. The purified monoethanolamine solution isintroduced into the drum 28 and fed through line 29 at a rate of 100gallons per minute. The pressure Within the vessel 19 is maintained at45 p.s.i.a. bottom, and the gas passing through the drip tank 39 andejector 40 produces a pressure of 20 pounds per square inch absolute inthe storage dnurn. A temperature of 270 F. and a pressure of 42 p.s.i.a.is maintained in the drip tank 35 and a temperature of 120- 130 F. and apressure of 17 p.s.i.a. is maintained in the accumulator 49. Materialfrom -the drip` tank flows into drum 28. The demineralized water isrecovered from line 50. The purified monoethanolamine entering the drum28 from vessel 19 contains less than .6 cu. ft. of CO2 per gallon ofamine and substantially no H28, thus illustrating the efficiency ofregeneration with the process of the invention. For conventionalregeneration, the amine will contain 1.5 cu. ft. of CO2 per gallon.

In Figures 3 and 4, I have shown a modification of the invention whereinthe contacting between a monoethanolamine treating solution and steamtakes place in a stripping column but the formation of corrosivedecomposition products is avoided due to the practically instantaneousheating by the use of a live steam as the reactivation agent and themaintenance of temperatures below 290 F. in all parts of the liquid. Inthe system illustrated by these gures, the rich amine enters through aline 80 `and passes through a heat exchanger 81 Where its temperature israised to a value within the range of 150 to 250 F. The heated materialis introduced to an intermediate tray of a stripping column 82 whilelive steam is introduced through nozzles 83 at the bottom of the columnby a valved line 84. Suitable conditions in the stripping column are atop temperature of 269 F., a bottom temperature of 274 F. and a bottompressure of 45 p.s.i.a. gage. The steam eiciently removes the acidiccompounds from the amine solution, and no undesirable decompositionproducts are formed due to the maintenance of a temperature within therange of 260 to 290 F.

The purified amine is Withdrawn from the bottom of the column and passedthrough a line 84 under the control of a motor valve 85 to a storagedrum 86. The motor valve 85 is operatively connected to a liquid levelcontroller 87 to control the rate of withdrawal of the amine solution soas to maintain a predetermined liquid level at the bottom of thestripper column. The purified monoethanolamne solution is withdrawn fromthe drum 86 by a line 88 having a pump 89 therein and returned to thegas purification step as required.

Condensate is added through a valved line 90 at the top of the column ata suicient rate to prevent loss of amine with the eiuent gas from thetop of the column.

The effluent, which is a mixture of steam, hydrogen sulfide and `otheracidic compounds passes through a line 91 and an ejector 92 having aline 93 extending into the drum 86. In this manner, the energy of thematerial leaving the top of the column is utilized to maintain a desiredreduced pressure in the storage drum 86.

The line 91 also includes a motor valve 95 which is operativelyconnected to a back pressure recorder controller 96 having a sensingelement 97 in the line 91. The unit 96 accurately controls the backpressure on Ithe stripper column 82.

From the motor valve and ejector 92, the overhead from the stripper 82passes through Ia cooler 99 and, thence, to a knock-out drum 100. In thedrum 100, the acidic compounds are taken overhead through la line 101,the back pressure being maintained constant on the column by a backpressure regulator 102 operatively connected to a motor valve 103 in theline 101 and having a sensing element 104 in the line 101. The acidicmaterials are passed to a are, or other disposal, as desired.

` A dsmneralized Water prodilvt @011cm at the bottom o f the drum 100and this water is withdrawn through `a 11ne 105 controlled by a motorvalve 106 operatively connected to a liqrlid `level controller 107 sothat the water is discharged at such a rate to maintain a predeterminedlevel in the drum 100.

The water leaving through line S is passed by a pump 108 and a line 109to any suitable facility for utilizing the water, a portion of the waterbeing returned through a line 110 to the fractionation column 100 underthe control of allow controller 111 operatively connectedto a motorvalve 112 in line 110 and having a sensing element 113 in the line 110.The column 100 is provided at its top with a mist extractor 115 toprevent carry over of liquid with the gaseous effluent containing acidiccompounds.

In the embodiment of Figures 3 and 4, it will be noted that the acidiccompounds are effectively stripped or removed from the rich aminesolution by contact with steam in the stripper vessel 82. Moreover, byvirtue of the fact that the contacting temperature is maintained withinthe range of 260 to 290 F., there is no decomposition of the aminesolution with resulting formation of extremely corrosive decompositionproducts. Hence, the contacting method of Figures 3 and 4 is quitesuperior to ordinary fractionation of the rich amine solution toseparate the acidic compounds therefrom. lIn such reactivations, if thetemperature, even at localized regions, rises to 300 F. or higher, aportion of the yamine decomposes as resulting formation of corrosivedecomposition products and resulting damage to the equipment in whichthe process is carried out.

While the invention has been described in connection with present,preferred embodiments thereof, it is lto be understood that thisdescription is illustrative only and is not intended to limit .theinvention.

I claim:

1. The process of vtreating an alkaline absorber solution utilized toremove absorbable acidic compounds constituting impurities from a gaswhich comprises contacting said solution with steam at a Itemperaturebelow the decomposition temperature of the absorber solution, re-

covering puriied absorber solution from the contacting step,transferring the purified absorber solution into a storage zone,withdrawing a gaseous effluent containing steam and said compounds fromthe contacting step, passing said stream through a path of restrictedcross section, and establishing communication lbetween said storage zoneand said path of restricted cross section, whereby passage of theeffluent through said path of restricted cross section produces areduced pressure in said storage zone.

2. The method of treating an alkaline absorber solution utilized 'forthe removal of absorbable acidic cornpounds constituting impurities froma gas which comprises contacting said absorber solution at an elevatedtemperature below the decomposition temperature of the solution withsteam, transferring purified absorber solution from said contacting zoneto a storage zone under reduced pressure whereby water is removed fromsaid absorber solution, passing 'a gaseous fraction from said contactingzone into an enlarged settling zone wherein a portion of the steam iscondensed and residual quantities of absorber solution are collected,passing the condensate to said storage zone, cooling the uncondensedmaterial, condensing the remainder of the steam, and recovering ademineralized water condensation product.

3. The method of treating an alkaline absorber solution utilized for theremoval of absorbable acidic compounds constituting impurities from agas which comprises contacting said absorber solution at an elevatedtemperature below the decomposition temperature of the solution withsteam containing a small amount of said compounds, thereafterconcurrently contacting the partially purified solution with pure steamto remove the remainder 0f Said @mounts transferring rr'ied ab- `sorbersolution from said contacting zone to a storage zone under reducedpressure whereby water is removed from said absorber solution, passing agaseous fraction from said contacting zone into an enlarged settlingzone wherein a portion of the steam is condensed and residual quantitiesof absorber solution are collected, passing the condensate to saidstorage zone, cooling the uncondensed material, condensing the remainderof the steam, and recovering a demineralized water condensation product.

4. The process of purifying an aqueous solution of monoethanolamineutilized to strip sulfur compounds from natural gas which comprisesheating said solution to a temperature within the range of ISO-250 F. inan indirect heat exchange zone free from decomposition of saidmonoethanolamine and contacting said heated monoethanolamine solutioncontaining sulfur compounds in a serarate zone with steam at atemperatureof 260 to 29 F.

5. The process of purifying an aqueous solution of monoethanolamineutilized to strip sulfur compounds from natural gas which comprisesheating said solution to a temperature within the range of 15G-250 F. inan indirect heat exchange zone free from decomposition of saidmonoethanolamine, contacting said heated monoethanolamne solutioncontaining sulfur compounds with steam at a temperature of 260 to 290 F.in a fractionation zone separate from said indirect heat exchange zone,recovering purified monoethanolarnine as a bottoms product, recoveringan overhead product containing steam and sulfur compounds, andcondensing said overhead product to separate water therefrom.

6. The method of purifying natural gas containing hydrogen sulfide whichcomprises contacting said natural gas with an aqueous solution ofmonoethanolamine, recovering natural gas free from hydrogen sulfide,withdrawing a rich monoethanolamine solution containing hydrogen sulfidefrom the contacting step, contacting said rich solution with steam at atemperature below 300 F., recovering purified absorber solution from thecontacting step, transferring the purified absorber solution to astorage zone, withdrawing a gaseous eluent containing steam `andhydrogen sulfide from the contacting step, passing said stream through apath of restricted cross section, and establishing communication betweensaid storage zone and said path of restricted cross section, wherebypassage of the eiliuent through said path of restricted cross sectionproduces a reduced pressure in said storage zone.

7. The method of purifying natural gas containing hydrogen sulfide whichcomprises contacting said natural gas with an aqueous solution ofmonoethanolamine, recovering natural gas free from hydrogen sulfide,withdrawing a rich monoethanolamine solution containing hydrogen sulfidefrom the contacting step, contacting said rich absorber solution at anelevated temperature below the decomposition tempera-ture of thesolution with steam, transferring purified absorber solution from saidcontacting zone -to a storage zone, passing a gaseous fraction from saidcontacting zone into an enlarged settling zone wherein a portion of thesteam is condensed and residual quantities of monoethanolamine arecollected, passing the condensate to said storage zone, cooling theuncondensed material, condensing the remainder of the steam, andrecovering a rdernineralized water condensation product.

8. The method of purifying natural gas containing hydrogen sufide whichcomprises contacting said natural gas with an aqueous solution ofmonoetl'ranolamine, recovering natural gas free from hydrogen sulfide,withdrawing a rich monoethanolamine solution containing hydrogen sulfidefrom the contacting step, contacting said rich absorber solution at anelevated temperature below the decomposition temperature of the solutionwith steam,

transferring purified absorber solution from saidzcontactving zone to astorage zone, passing a gaseous fraction from said-contacting zone intovam enlarged settling zone ering Ia demineralized water condensationproduct an accumulator zone, passing steam in indirect heat exchangeAwith said rich absorber solution to provide said elevated temperature,and establishing communication between Ithe -heat exchange zone thusdefined and the accumulator 8 vzoneV wherein said portion of4tllevsttirllll lisV condensed, there being an emlargedsteam trap zonein the path of comirnunication.',4 A i v- -f s. f Y, Referencesited inthe le of patent i' UNITED STATES PATENTS Randle-t Y 'ot. 2s, 1952

1. THE PROCESS OF TREATING AN ALKALINE ABSORBER SOLUTION UTILIZED TOREMOVE ABSORBABLE COMPOUNDS CONSTITUTING IMPURITIES FROM A GAS WHICHCOMPRISES CONTACTING SAID SOLUTION WITH STEAM AT A TEMPERATURE BELOW THEDECOMPOSITION TEMPERATURE OF THE ABSORBER SOLUTION, RECOVERING PURIFIEDABSORBER SOLUTION FROM THE CONTACTING STEP, TRANSFERRING THE PURIFIEDABSORBER SOLUTION INTO A STORAGE ZONE, WITHDRAWING A GASEOUS EFFUENTCONTAINING STEAM AND SAID COMPOUNDS FROM THE CONTACTING STEP, PASSINGSAID STREAM THROUGH A PATH OF RESTRICTED ACROSS SECTION, ANDESTABLISHING COMMUNICATION BETWEEN SAID STORAGE ZONE AND SAID PATH OFRESTRICTED CROSS SECTION, WHEREBY PASSAGE OF THE EFFUENT THROUGH SAIDPATH OF RESTRICTED CROSS SECTION PRODUCES A REDUCED PRESSURE IN SAIDSTORAGE ZONE.
 4. THE PROCESS OF PURIFYING AN AQUEOUS SOLUTION OFMONOETHANOLAMINE UTILIZED TO STRIP SULFUR COMPOUNDS FROM NATURAL GASWHICH COMPRISES HEATING SAID SOLTION TO A TEMPERATURE WITHIN THE RANGEOF 150-250*F. IN AN INDIRECT HEAT EXCHANGE ZONE FREE FROM DECOMPOSITIONOF SAID MONOETHANOLAMINE AND CONTACTING SAID HEATED MONOETHANOLAMIESOLUTION CONTAINING SULFUR COMPOUNDS IN A SEPARATE ZONE WITH STEAM AT ATEMPERATURE OF 260 TO 290*F.